Solar stills are used to distill water using a low standard technology. It is primarily available in two distinct types namely box stills and pit stills. Both these solar stills function with the heat supplied by the sun or more precisely from the heat of the soil. Solar stills are usually made available in these areas where there is no steady supply of clean water and rain or well water is next to impossible and an impractical approach. The water that is collected using the solar still is less in amount in normal conditions and this amount can further decrease if the water source is brackish or saline in nature. In case of water vapor, the vapor is cooled on a plastic coating sheet and then allowed to drop off in to a buried container which is set up with the help of a tube.
Learning the art of setting up a solar still is essential as it helps to generate a means of portable pure water in times of emergency. However they produce water in a limited quantity which is the biggest drawback of the device. A compromise method can be established by mixing the distill water with the brackish water content which in turn increases the amount. This water solution can be further purified using various methods. A more conventional approach to the problem of inadequate amount of water is to add fresh water or saline water along the edges of the solar still. This helps in increasing the final amount of the water content.
Solar still has been constantly put to use and development since 1551. It is a tried and tested a lot many times over the years and people have chosen this method as the most effective one in critical conditions. The first solar still was set up way back in 1872 in northern Chile. It was in the shape of a large basin and was effective in providing pure clean water to the nitrate miners. It made use of nearby brackish water as the source and distilled the water using blackened bottoms of long wood dye and alum. The statistics of water supply was pretty decent and went up to 5 kg of distilled water on a hot summer day which is equivalent to about 23000 liters per day. Due to the effectiveness of this plant, it is still in operation till date.
The production of water in a solar still is dependent upon the intensity of the solar energy that falls on the still. The Solar still efficiency (n) is calculated by calculating the ratio of the amount of energy that is utilized in vaporizing the water in the solar still to the amount of incident solar energy on the still. A solar still with higher efficiency is helpful as it provides a large amount of distilled water. The National Sanitation Foundation of USA makes use of the point of use technology to further remove any impurities such as arsenic and other chemicals.